Add sponsors system with time slider, LNbits invoices, and UX improvements

- Sponsors table, LNbits createInvoice, webhook handler
- Sponsor routes: create, homepage, list, my-ads, click, extend, check-payment
- Admin routes for sponsor management
- Frontend: SponsorForm, SponsorTimeSlider, SponsorCard, SponsorsSection
- Sponsors page, My Ads page, homepage sponsor block
- Header login dropdown with My Ads, Create Sponsor
- Transactions integration for sponsor payments
- View/click tracking
- OG meta fetch for sponsor images
- Sponsor modal spacing, invoice polling fallback
- Remove Lightning address and Category fields from sponsor form

Made-with: Cursor

backend/src/db/schema.sql

@@ -69,3 +69,29 @@ CREATE INDEX IF NOT EXISTS idx_quotes_expires_at ON quotes(expires_at);
 CREATE INDEX IF NOT EXISTS idx_quotes_status ON quotes(status);
 CREATE INDEX IF NOT EXISTS idx_deposits_created_at ON deposits(created_at);
 CREATE INDEX IF NOT EXISTS idx_deposits_lnbits_payment_hash ON deposits(lnbits_payment_hash);
+
+CREATE TABLE IF NOT EXISTS sponsors (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  npub TEXT NOT NULL,
+  title TEXT NOT NULL,
+  description TEXT NOT NULL,
+  image_url TEXT,
+  link_url TEXT NOT NULL,
+  category TEXT,
+  lightning_address TEXT,
+  invoice_id TEXT,
+  payment_hash TEXT,
+  price_sats INTEGER NOT NULL,
+  duration_days INTEGER NOT NULL,
+  status TEXT NOT NULL CHECK(status IN ('pending_payment','pending_review','active','expired','removed')),
+  created_at INTEGER NOT NULL,
+  activated_at INTEGER,
+  expires_at INTEGER,
+  views INTEGER DEFAULT 0,
+  clicks INTEGER DEFAULT 0,
+  extends_sponsor_id INTEGER
+);
+CREATE INDEX IF NOT EXISTS idx_sponsors_status ON sponsors(status);
+CREATE INDEX IF NOT EXISTS idx_sponsors_npub ON sponsors(npub);
+CREATE INDEX IF NOT EXISTS idx_sponsors_expires_at ON sponsors(expires_at);
+CREATE INDEX IF NOT EXISTS idx_sponsors_payment_hash ON sponsors(payment_hash);